The present invention relates to a procedure, and an apparatus for the implementation of said procedure, making it possible simply, effectively and rapidly, to check the physical state of trees, of wood and of wooden structures, and more particularly of poles (telephone poles, electrical poles, etc.), incorporating density variations, and, over time, exposed to the risk of biological degradation diminishing their initial properties.
There are, for example, millions of wooden poles in use in the world (10 million in France and 200 million in the United States, for example) which have to be periodically checked in order to maintain the lines, such as, for example, telephone and power lines, the main difference between these applications residing in the diameter of the poles which is smaller for telephone lines (of the order of 17 to 20 cm) than that of power lines (which is of the order of 20 to 40 cm).
One of the main problems which arises with such elements is that of periodically checking them, in order to verify their condition, so as to decide on maintenance and/or replacement operations, should this be necessary, for example if they present a risk of breaking, this being unacceptable given the fact that, at least as regards telephone poles, the personnel very often work by directly scaling the pole and that, every year, accidents happen, sometimes fatal accidents, because of the mechanical fragility of some of the supports.
Currently, the solution still commonly used to carry out such a check very often employs an empirical method based on the human ear, the checker giving the pole a few blows with a hammer and, depending on the acoustic response of the wood, determining a diagnosis on the state of the pole by virtue of his personal experience.
To date, many proposals have been made for carrying out such a check by means of a measurement apparatus, as emerges especially from U.S. Pat. Nos. 2,389,030, 4,343,179 and 4,249,414.
In general, the proposed solutions according to these documents consist in carrying out a local hardness measurement. In the case of the first document, the resistance to screwing a metal auger into the wood is measured, in the second, a "spike" is forced in linearly by a dynamometric system and finally, in the last case, the local hardness of the outer zone is measured so as to determine whether the pole exhibits the characteristics of being hard at the surface, and consequently of preventing the anchoring of a technician's grapplers for climbing, by means of a measurement assembly which penetrates slantwise into the perimeter, making an angle of a few degrees, with respect to the surface of the latter.
Such hardness measurements lack accuracy and reproducibility because they do not exclude penetration by the element into a crack due to drying-out of the pole. Moreover, they are dependent on a constant force which therefore leads to a variable penetration and to a diagnosis which is therefore never made with the same geographic coordinates.
In addition, the solutions described in these documents are very sensitive to diameter variations, the penetration of the auger or of the spike not always being made along the diametral axis, which leads to a measurement away from the natural radial axis of the wood and therefore constitutes an additional inaccuracy.
Finally, all the apparatuses proposed to date take into account just one factor enabling the residual strength of the wood to be checked, namely its hardness, and do not take into account a factor which is that of moisture content which can cause damage due to rotting of the pole and can weaken it at its center without giving any indication of weakness on the outside. In fact, since the poles are treated in an autoclave, the outer layer, which may go from 2 cm for spruce to 5 cm for pine, is more resistant over time. A single hardness measurement does not make it possible to detect whether damage is occurring, through the heart of the pole, and the weakening at its center, for example as a result of rotting.